SQOR and Sepsis: This results from dual mechanisms: (1) NADPH oxidase (NOX4)-derived ROS oxidize 63% of cysteine thiols in alveolar proteins (p < 0.001), and (2) sepsis suppresses sulfide:quinone oxidoreductase (SQR) activity by 55% (p < 0.05), impairing H2S detoxification (77).